The present disclosure relates to a metal line, and more particularly, to a metal line, a method of forming the metal line, and a display using the metal line, which can prevent an increase in resistance of a copper line.
A liquid crystal display (LCD), which is one type of flat display, includes a lower substrate having a gate line, a data line, a pixel electrode, a TFT, and the like, an upper substrate having a common electrode, and the like, and a liquid crystal layer disposed between the lower and upper substrates. In the LCD, a voltage is applied to the pixel electrode and the common electrode to generate an electric field across the liquid crystal layer, thus changing the orientation of the liquid crystal molecules of the liquid crystal layer. Therefore, the LCD displays an image by using such a change in orientation of the liquid crystal molecules and controlling the polarization of incident light.
To realize an LCD with high resolution in a large size, it is essentially required to reduce line resistance of a gate line or the like. For this reason, a metal line such as a gate line is formed of a low resistance material, for example, copper (Cu) or silver (Ag). Copper has a specific resistance ranging from 2.1 μΩcm to 2.3 μΩcm in a thin film state, which is about 30% lower than a specific resistance (3.1 μΩcm) of aluminum that is being widely used for a metal line. In addition, copper has a better electromigration resistance characteristic than aluminum so that copper exhibits good resistance against the formation of hillocks. Therefore, much attention is being paid on copper as a material for a metal line of a next generation device. However, copper has relatively poor adhesiveness with glass, and relatively good reactivity with silicon. Accordingly, before the formation of copper, an adhesion layer should be formed first or, alternatively, an adhesion layer and a diffusion barrier layer should be formed over and under the copper. Up to now, as a metal line structure of an LCD using a copper line, there has been proposed a bilayered metal line structure using an adhesive layer, for example, a bilayered structure of Mo/Cu, Mo—Ti/Cu, MoW/Cu or MoCr/Cu containing molybdenum (Mo) or Mo alloy. Alternatively, there has been also announced a trilayered structure using an adhesion layer and a diffusion barrier layer, for example, Mo/Cu/Mo or Mo/Cu/MoN.
In order to form an adhesion layer of Mo or Mo alloy, a process of forming the adhesion layer should be additionally performed besides a copper forming process, thus requiring an additional process apparatus. This leads to an increase in process time and a difficulty in wet etching. Hence, to reduce the process time and facilitate the wet etching, a stacked structure of CuO/Cu was recently proposed, in which a copper oxide (CuO) layer is formed under a Cu layer. This CuO/Cu stacked structure is advantageous in that a process time may be reduced and the wet etching may be easily performed because Cu and CuO layers are successively formed in the same apparatus.
Further, if a diffusion barrier layer is formed on the copper layer, the copper layer is not exposed so that it is possible to prevent an increase in resistance of the copper layer. In this case, however, another layer should be additionally formed besides the copper layer, thus requiring an additional process apparatus and increasing a process time.